Precise endpoint detection for etching processes

Abstract

A homogeneous marker is formed, possibly by the adsorption of trace amounts of an ambient material such as carbon monoxide gas, at a surface of a deposited material when the plasma in momentarily interrupted during plasma enhanced chemical vapor deposition or other deposition processes involving the presence of a plasma. When the deposited material is etched, the resulting crystal dislocations or adsorbed gas is detected as a marker by optical emission spectroscopy techniques. The accuracy of an end point determination of the etching process can be increased by providing a sequence of such markers within the bulk or volume of the deposited material. The markers, being merely an interface such as a slight crystal dislocation in otherwise homogeneous material, do not affect the electrical, chemical or optical properties of the remainder of the predetermined deposited material and thus the homogeneity of the deposited material is not significantly affected.

Description

1. Field of the InventionThe present invention generally relates to etching processes and, more particularly, to precision etching of deposited material in semiconductor structures.2. Description of the Prior ArtDue to the small size of elements of integrated circuits and the small minimum feature size of patterns of materials of which they are formed, many manufacturing process steps simultaneously deposit materials on or etch materials away from a plurality of masked areas over the entire surface of a chip or wafer. Many current, high performance semiconductor device designs also require the formation of layers of very precise thicknesses. Such thicknesses of material are usually formed by depositing a thicker layer and then etching it to the desired thickness. Such a technique allows more reliable formation of the layer which may not be continuous if merely deposited to the desired thickness.Among etching techniques, reactive ion etching (RIE) is very desirable due to its relativ...

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Problems solved by technology

However, the relatively high speed of the process decreases the accuracy with which the process may be controlled.

Further, the reactive ion etch process generally take a short but variable time to stabilize, once started, which increases the uncertainty as to the progress of the etching process.

This accuracy is insufficient to support the desired degree of consistency of integrated circuit element performance or even consistently high yield.

This approach, however, does not provide a solution to the above problem since the etched material is entirely removed and the etch stop material may not have the desired electrical properties.

This approach has several significant drawbacks, however.

The development of a three layer structure, itself requires a plurality of process steps and is expensive and time-consuming.

The etching of several layers of substantial thickness is also time consuming.

Any material added to the plasma from the etched surface may be redeposited and form undesired deposits or otherwise contaminate the semiconductor structure.

Further, the volume of nitride material removed and placed in the plasma does not allow precise determination of the completion of the removal of the nitride layer.

Finally, the ONO insulator and other layered structures are, by definition, inhomogeneous and may have electrical or optical properties which are undesirable or otherwise conflict with device designs.

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